Torsional vibration damper

ABSTRACT

Torsional vibration dampers for piston engines, particularly for motor vehicle engines, are mounted on the crankshaft of the engine in a torsionally resistant manner. The hub (2) bears a first flyring (3) which concentrically surrounds the hub and is connected to the outer surface of the hub (2) via a rubber spring device (5) acting in the peripheral direction. Furthermore, a second flyring is provided which is secured to the hub (2) via a rubber spring device (8), again acting in the peripheral direction. To allow a torsional vibration damper of this kind to damp all vibrations generated by the engine using simple means, the rubber spring device (5) bearing the first flyring (3) is rigid while the rubber spring device (8) of the second flyring (4), which is located radially outside the first flyring (3), is flexible. The outer flyring (4), which has a greater mass moment of inertia than the inner flyring (3), can be connected in parallel or in series with the inner flyring (3) via its rubber spring device (8).

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates to a torsional vibration damper for pistonengines, particularly for motor vehicle engines, with a hub which can bemounted in a torsionally resistant manner on the crankshaft of theengine, a first flyring which concentrically surrounds the hub and isconnected to the outer surface of the hub via a rubber spring deviceacting in the peripheral direction, as well as a second flyring which isdirectly or indirectly secured to the hub via a rubber spring device,again acting in the peripheral direction.

2. Prior Art

Known torsional vibration dampers of the aforementioned type, which aremounted directly on the output end of the crankshaft, serve to absorbthe engine vibrations induced by forces of inertia. These enginevibrations induced by forces of inertia are in the range ofapproximately 150 Hz to 650 Hz, depending on design.

In order to cover this entire range, several flyrings capable of motionrelative to each other are combined. In a known torsional vibrationdamper of the aforementioned type (DE-OS 36 08 420), for example,smaller flyrings, mounted in bearings inside the hub, are connected tothe main flyring via rubber spring devices.

In known systems, the low-frequency vibrations induced by gas forces,which are in the region of about 40 Hz to 100 Hz, are damped byadditional torsional vibration dampers attached to the end of thepropeller shaft.

In another known vibration damper (U.S. Pat. No. 3,670,593) the innerflyring is fixed at the hub and the outer flyring is connected with theinner flyring by an additional rubber spring. The rubber springs can bevaried in their length and in their properties for the respective task.This known construction only works in a good way if the outer flyringhas an essentially lower mass in respect to the inner flyring becauseotherwise the system can become unstable. Therefore the known vibrationdamper is very inflexible in respect to the frequencies to be coveredand especially there may be difficulties in damping the lower frequencyregion.

OBJECT AND SUMMARY OF THE INVENTION

Based on this state of the art the invention is based on the task ofmodifying the known vibration damper in such a way that all frequenciesoccurring at a motor especially the low-frequency vibrations induced bygas forces can be securely damped.

In accordance with the invention, the problem of the prior art isovercome by a rubber spring device bearing the first flyring which is ofrigid design and wherein, the outer flyring is mounted on the innerflyring in rotating fashion.

By this construction according to the invention it is possible toconduct the outer flyring exactly on the inner flyring which is situatedin a stable way by the rubber spring device being of rigid design.

The turning of mass is absolutely free. Therefore the outer flyring canbe equipped with a bigger mass without any problem. As a result of itsdesign features, the torsional vibration damper according to theinvention is in a position to cover the range of vibrations induced bygas forces as well, meaning that all vibrations generated in the enginecan be damped at the crankshaft. Thus, the vibrations are controlleddirectly at the point of origin. The equipment of a second aggregate fordamping the low-freqency vibrations therefore is unnecessary. Thetorsional damper according to the invention is not only of simplestructure, but also has the effect of preventing transmission from theoutset of low-frequency vibrations to the downstream units in thesystem.

Preferably between the outer flyring and the inner flyring in thebearing area a sliding bush is located. Therefore the mobility of theouter flyring on the inner flyring is limited.

To ensure a good vibration damping at motors where the low-frequentvibrations dominate, the outer flyring should preferably have a greatermass moment of inertia than the inner flyring.

Furthermore the rubber spring device bearing the second flyring can beof flexible design to hold the vibration efficiency of this outerflyring and to maintain a secure vibrational damping.

In order to make the rubber spring device bearing the outer flyringespecially flexible, this rubber spring device may have multiple breaksat regular intervals in the peripheral direction.

The torsional vibration damper according to the invention can bedesigned in such a way that the two flyrings sit directly on the hub viatheir rubber spring devices, i.e. are connected in parallel. In thiscase, the outer flyring can be secured via its rubber spring device to aradially projecting flange of the hub.

As an alternative, however, it is also possible to provide for seriesconnection of the flyrings in that the outer flyring is secured via itsrubber spring device to the outer area of the inner flyring.

The rubber spring device bearing the outer flyring preferably consistsof a bonded elastomer with a low modulus of shear.

The inner flyring is preferably connected to the hub via an all-round,continuous rubber layer.

The rubber spring device bearing the inner flyring preferably consistsof a non-bonded, pretensioned elastomer with a high modulus of shear.

So that the relatively large outer flyring can be guided accurately, itis expediently mounted on the inner flyring in rotating fashion. Asliding bush can be located between the outer and inner flyring in thebearing area.

The hub expediently consists of a lightweight material, such asaluminium or plastic, and has an integrally moulded part made of steel,grey cast iron or sheet metal for mounting on the crankshaft.

In addition, the side of the hub facing away from the flyrings may havean axial flange which is designed as a V-belt pulley or fitted with anattached V-belt-pulley.

BRIEF DESCRIPTION OF THE DRAWINGS

An example of the invention is illustrated in the drawings and describedin detail below on the basis of the drawings. The drawings show thefollowing:

FIG. 1: A view of one half of a torsional vibration damper.

FIG. 2: A section along line II--II in FIG. 1.

FIG. 3: A section, similar to FIG. 2, through another practical exampleof a torsional vibration damper.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT(S) OF THE INVENTION

According to FIGS. 1 and 2 in the drawings, torsional vibration damper 1comprises a hub 2, an inner flyring 3 and an outer flyring 4.

Inner flyring 3 is connected to the outer surface of hub 2 via rigidrubber spring device 5 which acts in the peripheral direction.

Rubber spring device 5, which bears inner flyring 3, is made of anon-bonded, pretensioned elastomer with a high modulus of shear.

Outer flyring 4 has a greater mass moment of inertia than inner flyring3 and is directly mounted in rotating fashion on an outer peripheralsurface of inner flyring 3 via sliding bush 6.

Hub 2 is provided with a radially projecting flange 7, by which outerflyring 4 is connected via a flexible rubber spring device 8 which actsin the peripheral direction. Rubber spring device 8 has multiple breaksat regular intervals in the peripheral direction and consists of abonded elastomer with a low modulus of shear.

Radial flange 7 of hub 2, which bears outer flyring 4, has an axialflange 9 on the side facing away from flyrings 3 and 4, this flangebeing fitted with an attached V-belt pulley 10.

Hub 2 consists of lightweight material, such as aluminium or plastic.For mounting the hub on a crankshaft not shown in the drawing, the hubis provided with an integral casting 11 made of harder material, such ascast steel or grey cast iron.

For mounting torsional vibration absorber 1 on the crankshaft, the hubis provided with axial bores 12, spaced at equal angles, which pass boththrough the material of hub 2 and through integral casting 11. Screwsare inserted through axial bores 12 and screwed into threaded bores in aradial flange located on the crankshaft.

In the practical example shown in FIG. 3, torsional vibration damper 13has approximately the same outside dimensions as torsional vibrationdamper 1, shown in FIGS. 1 and 2.

In contrast to the practical example shown in FIGS. 1 and 2, outerflyring 4a of torsional vibration damper 13 is not located on a flangeof hub 2a; instead, its rubber spring device 8a is secured to the outerarea of inner flyring 3a.

Inner flyring 3a is provided with a radial flange 14, on the outerperipheral surface of which the inner side of an axial flange 15 ofouter flyring 4a is borne via a sliding bush 16.

As in the practical example shown in FIGS. 1 and 2, rubber spring device8, which bears outer flyring 4, is made of a bonded elastomer with lowmodulus of shear. Rubber spring device 8a, which may have multiplebreaks at regular intervals, adheres both to the inner surface of outerflyring 4a and to the outer periphery of inner flyring 3a and to thefacing side of radial flange 14 on inner flyring 3a.

In this practical example, hub 2a again consists of a lightweightmaterial with an integral casting 11a for mounting on a crankshaft notshown in the drawing.

In this practical example, hub 2 is provided with an integrally moulded,one-piece V-belt pulley 17.

I claim:
 1. Torsional vibration damper for for motor vehicle engines,with a hub which is adapted to be mounted in a torsionally resistantmanner on a crankshaft of the engine, a first flyring whichconcentrically surrounds the hub and is connected to the outer surfaceof the hub via a first rubber spring device in a peripheral direction, asecond flyring concentrically and directly slidably mounted on anoutside of the first flyring, said second flyring being heavier thansaid first flyring, said second flyring concentrically surrounding thehub and secured to the hub via a second rubber spring device, in aperipheral direction, wherein the first rubber spring device (5) has amodulus of shear different from that of the second rubber spring device(8), the second flyring (4) being mounted on the first flyring (3) sothat the first flyring and the second flyring usually rotate togetherwith the hub while being capable of movement relative to each other. 2.Torsional vibration damper according to claim 1, wherein a sliding bush(6; 16) is located in a bearing area between the second flyring (4) andthe first flyring (3).
 3. Torsional vibration damper according to claim2, wherein the second flyring (4) has a greater mass moment of inertiathat the first flyring (3).
 4. Torsional vibration damper according toclaim 3, the second rubber spring device (8) has a lower modulus ofshear than the first rubber spring device (5).
 5. Torsional vibrationdamper according to claim 4, the second rubber spring device (8) iscomposed of a plurality of rubber elements equiangularly spaced aroundthe circumference of the flyring (4).
 6. Torsional vibration damperaccording to claim 5, wherein the second flyring (4) is secured via thesecond rubber spring device (8) to a radially projecting flange (7) ofthe hub (2) and to an outer area of the first flyring (3).
 7. Torsionalvibration damper according to claim 6, the second rubber spring device(8) is made of bonded elastomer with a lower modulus of shear than thefirst rubber spring device (5).
 8. Torsional vibration damper accordingto claim 7, wherein the first flyring (3) is connected to the hub (2)via a continuous annular layer.
 9. Torsional vibration damper accordingto claim 8, wherein the first rubber spring device (5) bearing the innerflyring (3) is made of non-bonded, pretensioned elastomer with a highermodulus of shear than the second rubber spring device (8).
 10. Torsionalvibration damper according to claim 1, wherein the second flyring (4)has a greater mass moment of inertia than the first flyring (3). 11.Torsional vibration damper according to claim 1, wherein the hub (2)comprises an outer part made of a lightweight material and an integralmoulded inner part (11) made of steel, grey cast iron or sheet metal formounting on a crankshaft.
 12. Torsional vibration damper according toclaim 1, wherein a side of the hub (2) facing away from the firstflyring and the second flyring (3, 4) has an axial flange which isdesigned as a V-belt pulley (17) or is fitted with an attached V-beltpulley (10).
 13. Torsional vibration damper according to claim 1 whereinthe second rubber spring device (8) has a lower modulus of shear thanthe first rubber spring device (5).
 14. Torsional vibration damperaccording to claim 13, wherein the second rubber spring device (8) iscomposed of a plurality of rubber elements equiangularly spaced aroundthe circumference of the second flyring (4).
 15. Torsional vibrationdamper according to claim 1, wherein the second flyring (4) is securedvia the second rubber spring device (8) to a radially projecting flange(7) of the hub (2).
 16. Torsional vibration damper in according to claim1, wherein the second flyring (4) is secured to the hub via the secondrubber spring device (8) being engaged on an outer area of the firstflyring (3).
 17. Torsional vibration damper according to claim 1,wherein the second rubber spring device (8) is made of a bondedelastomer with a low modulus of shear.
 18. Torsional vibration damperaccording to claim 1, wherein the first inner flyring (3) is connectedto the hub (2) via a continuous annular layer.
 19. Torsional vibrationdamper according to claim 1 wherein the first rubber spring device (5)is made of a non-bonded, pretensioned elastomer with a modulus of shearhigher than that of the second rubber spring device (8).
 20. Torsionalvibration damper for motor vehicle engines, with a hub which is adaptedto be mounted in a torsionally resistant manner on a crankshaft of theengine, a first flyring which concentrically surrounds the hub and isconnected to the outer surface of the hub via a first rubber springdevice in a peripheral direction, a second flyring concentrically anddirectly slidably mounted on an outside of the first flyring, saidsecond flyring being heavier than said first flyring, said secondflyring concentrically surrounding the hub and secured to the hub via asecond rubber spring device in a peripheral direction, wherein the firstrubber spring device (5) has a modulus of shear different from thesecond rubber spring device (8), the second flyring (4) being mounted onthe first flyring (3) so as to usually rotate together with the hubwhile being capable of movement relative to each other,wherein thesecond flyring (4) has a greater mass moment of inertia than the firstflyring (3), and wherein the second rubber spring device (8) bearing thesecond flyring (4) has a low modulus of shear.
 21. Torsional vibrationdamper according to claim 20, wherein the hub (2) comprises an outerpart made of a lightweight material an integrally moulded inner part(11) made of steel grey cast iron or sheet metal for mounting on acrankshaft.